The increasing carbon dioxide concentration in the atmosphere is suggested to be linked to increasing temperatures and changes in the World's climate, and significant interest has been given to CO2 capture, especially from combustion gases. One well established CO2 capture method uses a chemical solvent (typically amine based) to absorb CO2 from flue gas. This method is effective, however presents several difficulties: (1) solvents must be manufactured, purchased, and transported, resulting in significant expenses; (2) most solvents (and especially amine solvents) tend to degrade via oxidative and/or thermal pathways. As a consequence the solvent must be maintained and/or continuously replaced; and (3) some solvents present environmental concerns as they may form harmful compounds once emitted to the atmosphere.
Other known CO2 capture processes may circumvent at least some of these drawbacks, including PSA (pressure swing adsorption) or membrane processes. However, these processes are often costly because they carry energy penalties caused by the regeneration of CO2 loaded adsorbents or by the need for recompression of flue gas upstream of a membrane.
CO2 can also be removed from a gas stream based on the principles of cryogenic removal or desublimation. For example, U.S. Pat. Pub. No. 2011/0226010 teaches separation of CO2 from flue gas by compression, expansion and refrigeration. While such process is at least conceptually attractive, significant energy requirements often render such separation impracticable. This and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Also, where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
In another example, as described in U.S. Pat. No. 4,265,088, CO2 is frozen out from a gas stream, and so isolated solid CO2 is then sublimated after it has been deposited in a tower. Such configuration, however, is typically not able to generate a pure CO2 stream and requires in most cases substantial quantities of energy for CO2 recovery. Similarly, U.S. Pub. No. 2011/0023537 teaches desublimation of CO2 on porous media and CO2 recovery via fluid CO2 to so produce a warm porous medium. However, use of such porous media may be problematic due to potential clogging. Furthermore, CO2 recovery using liquid CO2 as described in the '537 reference is not energy efficient under various circumstances.
Thus, there is still a need for energy efficient systems and methods of capture of CO2 from a flue gas by cryogenic desublimation, and a further need for the removal of the solid CO2.